Some aspects of the biogenesis of tRNA and mRNA from primary gene transcripts to their final functional form in both E. coli and human KB cells will be investigated. Studies of tRNA function in E. coli will also be undertaken through an investigation of codon-anticodon recognition in vivo and the role of rare nucleotides in protein synthesis. An attempt will be made to answer the following questions: a) how do changes in the nucleotide sequence of precursor tRNAs affect their interaction with RNase P? b) Is the pathway of tRNA biogenesis in human cells analogous to that found in E. coli? c) Are endoribonucleases important in post-transcriptional regulation of gene expression in E. coli and human cells? d) Are endoribonucleases, specific for unstable RNAs, part of the ribosome in E. coli? Does message context play a major role in affecting suppression of amber and ochre nonsense mutations in vivo? f) Can the absence of any particular nucleotide modification of tRNATyr drastically affect its ability to carry out protein synthesis in vitro? BIBLIOGRAPHIC REFERENCES: S. Altman and V. Warner, Acridine Mutagenesis of Bacteriophage T4 Intracellular DNA. Molec. Gen. Genetics 138 (1975) 333-343. S. Altman, A Modified Uridine in the Anticodon of E. coli tRNAtyr suoc. Nucleic Acids Res. (1976) in press.